Add function to convert a Dato ID (Base64-encoded, URL-safe) back to a regular v4 UUID hex string

[arcataroger]

Simple function that reverses our special encoding. Given an generated ID like WTyssHtyTzu9_EbszSVhPw, it will return 593cacb0-7b72-4f3b-bdfc-46eccd25613f.

[stefanoverna]

As I was saying, I don't think we need to expose a function that converts to a classic UUID format. We don't use such format at all. It seems more useful to me to offer a validateId() function instead, which documents what we consider a valid ID, so that if someone wants to generate IDs manually, they can verify that they are correctly formatted.

[arcataroger]

Thanks for the changes @stefanoverna! I also didn't realize you could just forcibly rewrite the commit history like that (instead of adding to it)... 👀

Every year I use Git, I understand it a little less, lol